Infrared Spectrometry Flashcards
Spectroscopic Analysis Function
Quality control for regulatory bodies and published standards (pharmacopia)
Pharmaceutical Impurities Sources
Manufacturing, product degradation, packaging and microbiological contaminants
How impurities are separated and analysed
Purified by chromatography. Analysed by spectroscopy and spectrometry
How Infrared is perceived to humans
Not visible (wavelength too long), perceived as heat. The greater the heat, the more IR radiated
Thermography Def
Measures heat released
IR Spectroscopy Def
Qualitative Identification. Identifies functional groups by bond vibrations, characterises solid samples and water content is measured. IR spectra are unique to each functional group
UV Spectroscopy
electron transitions determine bonding patterns
Nuclear Magnetic Resonance Spectroscopy
Detects H atom signals and distinguishes isomers
Melting Point and purity
Melt sample. The narrower the range of temps melted over = the more pure the sample
Which C double bond is longer acid or ester
acid
Which is longer C double bond or OH
C double bond
Relationship between wavelength and frequency
bigger wavelength = smaller frequency
How adding energy to bond impacts it
It stretches or changes angle
Stretching Def
Changing of bond length. 2 Types
Symmetric stretching def
All bonds lengthen and shorten at the same time
Asymmetric Stretching def
When half the bonds lengthen the other half shortens
Changing of bond angles
Angles changes in relation to body and substituents. 4 Types
In plane Outline
Both bonds move left and then right at the same time
Scissoring Outline
Bond angle move together at the same time and then apart
Out of Plane Wagging
Both bond move closer to main body of molecule and away
Out of plane twisting
1 bond moves away from the body of molecule and 1 moves nearer
Which is longer stretching or bending
bending frequencies are lower then stretching
Which bond angles are longer
rock > scissor > wag
Which stretching is longer
Asymmetric > symmetric. Symmetric is lower frequencies then assymetric
IR Activity Rules
IR absorption causes bending if there’s a change in dipole moment. Thus homonuclear (2 atoms are the same) don’t vibrate
Linear (no branching) number of fundamental; vibrations
3(no of atoms) - 5
Non-linear (branched) no. of fundamental vibrations
3(no of atoms) - 6
Water Vibrational Nodes
symmetric (3652 cm^-1), bends (1,595 cm^-1, longer), asymmetric angles (3,756 cm^-1)
Deformation Def
The functional groups move away from and towards each other. Umbrella like movement
Skeletal Vibrations Range
1400 - 600 cm^-1. This is the fingerprint region
Bond strength
triple bond > double bond > single bond
Relationship between vibrational frequency (n bar) and mass of 2 atoms (mew bar)
vibrational frequency is inversely proportional to mass
Relationship between force constant (strength of bond) (k) and vibrational frequency
As strength of bond increases, vibrational frequency decreases
Calculation for bond frequency
v bar = 1/(2(pi)c) x (k/mew)^1/2
How do frequencies tend to move across the x-axis
Frequencies decrease movinf feom left to right
What influences frequency range (breadth of bands)
Hydrogen Bonding
Why might alkene and alkynes be represented in chart
Obscured by other absorbances in region and bands are of bare and medium intensity
How do you increase the strength of absorption in alkynes
If they are asymmetric
Why are carbonyl bands so broad
Reactive in nucleophilic addition. Ketones, aldehydes and amines are lower. Usually longest signal
Steps for analysing IR chart if C double bond O is present
Check OH (carboxylic acid), check NH (amide), check C-O (ester)
Steps for analysing IR chart if no C double bond O
Check OH (alcohol), check NH (amine), check C-O (ester), look C double bond (aromatic)
Conjugate bonds Def
Molecules with atoms with both single and double bonding
Relationship between conjugation and frequency absorption
More conjugation = lower absorption (electrons move from bond to bond). Aromatic is lowest
Relationship between electrons in s and p orbitals and frequency absorption
more electrons =absorbs at higher frequency
